Continuous process for the removal of monomeric impurities from aqueous dispersions of homo- and copolymers of vinyl chloride

Abstract

In a process for removing monomeric impurities from an aqueous dispersion of homopolymers or copolymers of vinyl chloride having a surface tension below 60 dyn/cm. by treatment with steam while avoiding foam formation by a rapid lowering of the pressure at high flow velocities, the improvement which comprises: (a) continuously mixing said dispersion in a flow pipe with steam at a steam pressure of 800-4660 millibars for an average residence time of about 0.01-5 seconds; (b) continuously passing the resultant admixture from said flow pipe at a velocity of at least 30 meters per second directly to a degasification vessel having a pressure of 133-660 millibars; and (c) continuously recovering a polymer product containing less than 20 p.p.m. residual monomer impurities therefrom.

What is claimed is: 
     
       1. In a continuous process for removing monomeric impurites from an aqueous dispersion of homopolymers or copolymers of vinyl chloride having a surface tension below 60 dyn/cm. by treatment with steam while avoiding foam formation by a rapid lowering of the pressure at high flow velocities, the improvement which comprises: (a) continuously mixing said dispersion in a flow pipe with steam at a temperature of 120°-143° C. and corresponding steam pressure of 1950-3930 millibars for an average residence time of about 0.01.5 seconds;   (b) continuously passing the resultant admixture from said flow pipe at a velocity of at least 30 meters per second directly to a degasification vessel having a pressure of 133-660 millibars; and   (c) continuously recovering a stable polymer dispersion containing less than 20 p.p.m. residual monomer impurities therefrom.   
     
     
       2. A process according to claim 1, wherein the weight ratio of steam:dispersion is 1:2 to 1:30 and the steam is saturated. 
     
     
       3. A process according to claim 2, wherein said ratio is about 1:10. 
     
     
       4. A process according to claim 1, wherein the exit velocity of said admixture from the flow pipe is 30-100 m./sec.